In the field of vehicle drivetrain components, a transfer case is an apparatus that distributes driving power to more than one driven axle of the vehicle. A typical transfer case receives driving power from the transmission of the vehicle and transfers that power to a primary output shaft and a secondary output shaft, with the secondary output shaft being driven selectively using a clutch. In addition, two speed transfer cases provide gear reduction to allow operation in a high range, which is typically a 1:1 drive ratio, or a low range, such as a 2:1 drive ratio.
Many of the components in a transfer case require lubrication and/or fluid pressure for hydraulic actuation. For example, in some transfer cases, a mode shift between a two-wheel drive mode and a four-wheel drive mode is performed by a hydraulically actuated clutch that requires pressurized hydraulic fluid in order to operate.
In order to pressurize the hydraulic fluid in the transfer case, the transfer case includes a pump. The fluid is directed to an inlet of the pump, where it is pressurized by the pump. The pressurized fluid is supplied to the components of the transfer case (e.g. by a passageway formed through a shaft), and then returns to a sump formed in the transfer case. When a vehicle is in motion, however, the forces experienced by the vehicle can cause the hydraulic fluid to move in a manner that prevents a constant flow of fluid into the inlet of the pump. If the pump is not receiving enough fluid at its inlet, pump starvation occurs, and the output of the pump may not be sufficient to lubricate and/or actuate components of the transfer case.